Field
An electrode wound element for a non-aqueous electrolyte rechargeable battery, a non-aqueous electrolyte rechargeable battery, and a method of preparing the electrode wound element for a non-aqueous electrolyte rechargeable battery are provided.
Description of the Related Art
Research on a polyvinylidene fluoride (PVDF)-based fluorine resin as a matrix polymer of a gel electrolyte for a rechargeable lithium ion battery has been actively made. For example, technology of forming a porous layer made of the PVDF-based fluorine resin on the surface of a separator is widely known. In this technology, the porous layer is, for example, formed on the surface of the separator in the following methods.
A first method includes preparing a slurry by dissolving a fluorine resin in an organic solvent such as NMP (N-methyl pyrrolidone), dimethyl acetamide, acetone, or the like, coating the slurry on a separator or an electrode, and phase-separating the fluorine resin by using a poor solvent such as water, methanol, tripropylene glycol, or the like or vapor thereof to form a coating layer in which the fluorine resin is made porous.
A second method includes preparing a thermal slurry by dissolving a fluorine resin in a heating electrolytic solution using a solvent such as dimethyl carbonate, propylene carbonate, ethylene carbonate, and the like to prepare heated slurry, coating the heated slurry on a separator or an electrode to prepare a coating layer, cooling down the coating layer, and transferring the fluorine resin into a gel (a porous layer swollen by an electrolyte solution).
However, the separator having the PVDF porous layer on the surface in the above method has insufficient slipperiness when compared to a separator having no porous layer and easily becomes electrostatic and thus is difficult to handle in a preparing process. Specifically, when the separator is overlapped with belt-shaped positive and negative electrodes for a wound element, the wound element becomes deformed due to the insufficient mutual slipperiness of the separator. When the wound element is deformed, the wound element is difficult to be inserted into a case. In addition, a non-aqueous electrolyte rechargeable battery using this deformed wound element may have an insufficient cycle-life.
In addition, recently, in order to suppress thermal shrinkage of a separator when being heated, a heat-resistance filler is added to a porous layer. However, when the heat-resistance filler is added in an amount that is necessary for suppressing thermal shrinkage of a porous layer, interface adherence between the separator and the electrode of a non-aqueous electrolyte rechargeable battery may be deteriorated. Therefore, the following problems may occur.
In a method of preparing a wound element, a wound element is pressed while heating and thereby made to be flat in order to integrate a separator, a porous layer (gel electrolytic layer) and each electrode. In order to reduce unfavorable effects on the wound element, the wound element is pressed at a low temperature and a low pressure. For example, since an electrolyte solution is weak for a high temperature, the wound element needs to be pressed at a low temperature considering unfavorable effects on the electrolyte solution.
However, since a heat-resistance filler physically suppresses thermal shrinkage of a porous layer, its fluidity in an adhesive layer is not good. When the porous layer includes a heat-resistance filler particle, it does not flow even though the wound element is pressed at a low temperature and a low pressure. Therefore, sufficient adhesion interface is not formed on the porous layer, and the porous layer is not adhered to each electrode. That is, adherence between the separator and each electrode is not sufficient.
On the other hand, Japanese Patent Laid-Open Publication No. Hei. 10-110052, Japanese Patent Laid-Open Publication No. 2012-190784, Japanese Patent Publication No. 2010-538173, and Japanese Patent Laid-Open Publication No. 2011-204627, for example, disclose technology of using fluorine resin particles or ceramic particles. Japanese Patent Laid-Open Publication No. Hei. 10-110052 discloses a method of protruding a part of the fluorine resin particles out of a porous film separator. Japanese Patent Laid-Open Publication No. 2012-190784 discloses a method of including the ceramic particles inside a separator. Japanese Patent Laid-Open Publication No. 2010-538173 discloses a method of charging a part of micropores in a non-woven fabric with the fluorine resin particles. Japanese Patent Laid-Open Publication No. 2011-204627 discloses a method of preparing a negative electrode by using aqueous slurry in which a polymer complex of a fluorine resin and a polymer having an oxygen-containing functional group is dispersed. However, these methods do not solve the aforementioned problem at all.